The present invention relates generally to turbine engine blades and, more particularly, to a turbine blade tip peripheral end wall with a grooved cooling arrangement.
A reduction in turbine engine efficiency results from leaking of hot expanding combustion gases in the turbine across a gap between rotating turbine blades and stationary seals or shrouds which surround the blades. The problem of sealing between such relatively rotating members to avoid loss in efficiency is very difficult in the turbine section of the engine because of high temperatures and centrifugal loads.
One method of improving the sealing between a respective turbine blade and shroud is the provision of squealer type tips on turbine blades. A squealer tip includes a continuous peripheral end wall of relatively small height typically surrounding and projecting outwardly from an end cap on the outer end of a turbine blade that encloses a cooling air plenum in the interior of the blade.
During operation of the engine, temperature changes create differential rates of thermal expansion and contraction on the blade rotor and shroud that may result in rubbing between the blade tips and shrouds. Centrifugal forces acting on the blades and structural forces acting on the shrouds create distortions thereon that may also result in rubbing interference.
Such rubbing interference between the rotating blade tips and surrounding stationary shrouds causes heating of the blade tips resulting in excessive wear or damage to the blade tips and shrouds. Heating produced by the leakage flow of hot gases may actually be augmented by the presence of a cavity defined by the end cap and peripheral end wall of the squealer tip because of the increased surface area of the peripheral end wall. The peripheral end wall is especially difficult to cool, because the end wall extends away from the internally cooled region of the blade. Therefore, squealer type blade tips, though fostering improved sealing, actually require additional cooling.
Because of the complexity and relative high cost of replacing or repairing turbine blades, it is desirable to prolong as much as possible the life of blade tips and respective blades. Blade tip cooling is a conventional practice employed for achieving that objective. The provision of holes for directing air flow to cool blade tips is known in the prior art, for instance as disclosed in U.S. Pat. No. 4,247,254 to Zelahy, and have been applied to squealer type blade tips as disclosed in U.S. Pat. No. 4,540,339 to Horvath.
Turbine engine blade designers and engineers are constantly striving to develop more efficient ways of cooling the tips of the turbine blades to prolong turbine blade life and reduce engine operating cost. Cooling air used to accomplish this is expensive in terms of overall fuel consumption. Thus, more effective and efficient use of available cooling air in carrying out cooling of turbine blade tips is desirable not only to prolong turbine blade life but also to improve the efficiency of the engine as well, thereby again lowering engine operating cost. Consequently, there is a continuing need for a cooling hole design that will make more effective and efficient use of available cooling air.
A turbine assembly having at least one rotor blade comprises an airfoil having a pressure sidewall, a suction sidewall, and a tip portion having a tip cap. A squealer tip is disposed on the tip cap. A plurality of blade tip cooling holes are positioned within the airfoil near the tip portion. Cooling grooves are disposed within the airfoil to connect the blade tip cooling holes with the top portion of the squealer tip to transition cooling flow from the cooling holes to the tip portion.